This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
ACCS autonomous component carrier selection
BIM background interference matrix
CA carrier aggregation
CC component carrier
C/I carrier interference ratio
DL downlink (eNB to UE)
eNB E-UTRAN Node B (evolved Node B/base station)
E-UTRAN evolved UTRAN (LTE)
IMT international mobile telecommunications
ITU-R international telecommunication union-radio
LTE long term evolution
LTE-A LTE advanced
MM/MME mobility management/mobility management entity
OLPC open loop power control
PC power control
PDCCH physical downlink control channel
PRB physical resource block
PSD power spectral density (dBm/Hz)
RRC radio resource control
RRAT radio resource allocation table
SINR signal to interference plus noise ratio
UE user equipment
UL uplink (UE to eNB)
UTRAN universal terrestrial radio access network
In the communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE, E-UTRA), the LTE Release 8 is completed, the LTE Release 9 is being standardized, and the LTE Release 10 is currently under development within the 3GPP. In LTE the downlink access technique is orthogonal frequency division multiple access OFDMA, and the uplink access technique is single carrier frequency division multiple access SC-FDMA. These access techniques are expected to continue in LTE Release 10.
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, V8.6.0 (2008-09), and shows the overall architecture of the E-UTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an evolved packet core, more specifically to a MME and to a Serving Gateway. The S1 interface supports a many to many relationship between MMES/Serving Gateways and the eNBs.
Of particular interest herein are the further releases of 3GPP LTE targeted towards future IMT-Advanced systems, referred to herein for convenience simply as LTE-Advanced (LTE-A). LTE-A is directed toward extending and optimizing the 3GPP LTE Release 8 radio access technologies to provide higher data rates at very low cost. LTE-A will most likely be part of LTE Release 10. LTE-A is expected to use a mix of local area and wide area optimization techniques to fulfill the ITU-R requirements for IMT-Advanced while keeping the backward compatibility with LTE Release 8.
There is a bandwidth extension beyond 20 MHz in LTE-Advanced which is to be done via carrier aggregation (CA). This is shown conceptually at FIG. 1B in which there are five CCs aggregated to form one larger LTE-Advanced bandwidth of 100 MHz. Each CC has DL and UL resources for enabling increased data rates such as for example by simultaneously scheduling an active UE across multiple CCs to better distribute traffic.
In general for the LTE-A CA concept, at least one of the CCs is a stand-alone CC and so is backwards compatible with 3GPP Release 8 UEs. LTE-A terminals can receive or transmit simultaneously on multiple aggregated CCs. Each CC in the overall bandwidth may be a Release 8 compatible stand alone CC, or some may be stand alone but not Release 8 compatible (e.g., violating the LTE Release 8 fixed duplex gap), and further some may be extension carriers which cannot exist stand-alone and which are tied to a stand-alone CC. While the example at FIG. 1B illustrates 5 CCs of 20 MHz each spanning a total contiguous bandwidth of 100 MHz, other embodiments of CA may have non-contiguous CCs and/or CCs which do not even belong the same frequency band (for example the spectrum blocks might even be far apart in terms of frequency such as 700 MHz and 2.1 GHz). Other CA embodiments may have an asymmetric DL/UL CA which for example may be built by combining a frequency division duplex FDD carrier with a time division duplex TDD carrier. LTE-A is an exemplary but not the only CA-type system.
Another aspect being developed in LTE-A is the concept of heterogeneous networking, or HetNet for short. Adjacent cells cooperate to achieve more efficient use of scarce radio resources even if they are different wireless systems. For example, there may be femto-cells, sometimes termed home base stations or other networks of one cell or very limited geographic area, existing side by side with other femto-cells and with traditional network-operated cellular base stations/eNBs. These cells may cooperate to mitigate interference with one another, or at least positively limit their own interference to adjacent cells to avoid the greedy cell scenario in which one cell occupies more bandwidth resources than its traffic justifies, at the expense of an adjacent cell.
ACCS is one of the CA interference management schemes that is proposed for LTE-A. The following published documents give some background on ACCS; particularly as it relates to LTE-A, and are attached to the above-referenced priority US provisional application as respective Exhibits A through E.    L. Garcia, K. I. Pedersen, P. E. Mogensen, “AUTONOMOUS COMPONENT CARRIER SELECTION: INTERFERENCE MANAGEMENT IN LOCAL AREA ENVIRONMENTS FOR LTE-ADVANCED”, IEEE Communications Magazine, September 2009.    R1-093321, “AUTONOMOUS CC SELECTION RESULTS FOR DENSE URBAN AREA”    R1-094659, “AUTONOMOUS CC SELECTION FOR HETEROGENEOUS ENVIRONMENTS”    R1-090235, USE OF BACKGROUND INTERFERENCE MATRIX FOR AUTONOMOUS COMPONENT CARRIER SELECTION FOR LTE-ADVANCED.     L. Garcia, K. I. Pedersen, P. E. Mogensen, “AUTONOMOUS COMPONENT CARRIER SELECTION FOR LOCAL AREA UNCOORDINATED DEPLOYMENT OF LTE-ADVANCED”, accepted for publication in IEEE Proc VTC 2009-Fall.
As described in the above references, the ACCS concept relies on collection of the so-called background interference matrix (BIM) at each base station. The BIM is used by the base stations to determine if it is allowed to take additional component carriers (CCs) into use without causing too low performance/too much interference in the surrounding cells using the same CC. The BIM can also be used to ensure that the performance in the host cell is acceptable. Most of the previous ACCS studies have focused on the downlink BIM and assume that the uplink BIM is sufficiently close to the downlink BIM that the two can be interchanged. The inventors have found that the UL BIM is regularly biased and so the DL BIM is not an accurate substitute.